AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
In situ Ambient Pressure XPS Investigations of PdAg Alloy Nanoparticles: Towards Cheaper Catalysts
MARIA E MESSING, Sara Blomberg, Natalia M Martin, Johan Gustafson, Jesper Andersen, Lars Erik Walle, Anne Borg, Henrik Grönbeck, Michael E Grass, Zhi Liu, Edvin Lundgren, Knut Deppert, Lund University
Abstract Number: 422 Working Group: Nanoparticles and Materials Synthesis
Abstract Due to the huge economic and environmental rewards, one major goal in catalysis related research is to create cheaper catalysts. As catalysis happens on the surface of the catalyst, one possible way to realize this would be to dilute the more expensive active material with a less costly one, providing that the active material stays at the surface. This could be achieved by using a material which is less prone to interact with the reactant gases, such as a cheaper noble metal. In most catalysts, the active material is dispersed in a high area complex oxide support as nanoparticles. In order to maintain the high activity, it would be necessary to ensure that the active material is at the surface of the nanoparticle.
We report on our findings from attempts to produce PdAg alloy particles using aerosol generation. The use of PdAg is motivated by the fact that Pd segregates to the surface in the presence of a reactive gas while Ag segregates in ultra-high vacuum (UHV) and that Ag is considerably less expensive than Pd.
TEM images reveal that most particles are single crystalline. From XEDS the composition are measured to approximately 75 atomic% Pd and 25 atomic% Ag. Ag 3d$_(5/2) core level XPS spectra from the PdAg particles are compared to the corresponding spectra of a Pd$_(75)Ag$_(25) (100) single crystal and a (110)-oriented Ag crystal. The Ag 3d$_(5/2) binding energy for the nanoparticles compares well with the bulk contribution for Pd$_(75)Ag$_(25) (100) which in turn is shifted by 0.5eV relative to the bulk value in pure Ag. From this observation, we therefore conclude that the PdAg alloy particles consist of a proper alloy and not Ag and Pd in separate phases. In addition, corresponding Pd 3d spectra strongly indicate that the active Pd is present at the surface of the PdAg particles in the presence of reactant gases.